The present invention generally relates to temperature control systems for maintaining the temperature of an electronic device at a predetermined temperature while the device is being tested.
Testing equipment has been utilized in the electronics industry to test the operation of integrated circuits and other electronic devices maintained at a predetermined temperature. Generally, the testing equipment will include a thermal head having a temperature controlled surface for contacting the electronic device being tested. The thermal head is simultaneously heated and cooled in an attempt to maintain the predetermined temperature. The test equipment users (i.e., electronic device manufacturers) generally specify that the thermal head be capable of maintaining the predetermined temperature under all conditions with a variance of xc2x13xc2x0 C.
With some such testing equipment, the predetermined temperature can be varied at the option of the technician conducting the testing procedure. Thus, electronic devices can be tested at multiple temperatures to simulate a wide variety of operating conditions. In order to produce the desired temperature at the thermal head, these devices have circulated a chilled liquid, such as water or ethylene glycol, through the thermal head. The liquid itself is chilled in a heat exchanger including the evaporator of a separate refrigeration system. In other words, the evaporator is cooled by the refrigeration system, which then serves to chill the circulating liquid. Heat may be added by heating elements incorporated into the thermal head when necessary to maintain the predetermined temperature.
This prior art technique of using a separate liquid loop presents a number of significant disadvantages. For example, additional maintenance requirements are contributed by the presence of the liquid loop. Moreover, the entire xe2x80x9ccool sidexe2x80x9d of the liquid loop will often be below dew point, thus requiring extensive insulation. Often, it takes systems utilizing a liquid loop up to an hour to reach the desired temperature before testing can begin. The liquid loop also increases the size and power consumption requirements of the testing system.
In one aspect, the present invention provides an apparatus for controlling the temperature of an electronic device under test. The apparatus comprises a thermal head having a temperature controlled surface for making thermal contact with the electronic device. The thermal head defines a flow channel for passage of a refrigerant fluid so as to cause transfer of thermal energy between the electronic device and the thermal head.
The apparatus further includes a refrigeration system in fluid communication with the flow channel of the thermal head to supply refrigerant fluid thereto. The refrigeration system includes a metering valve operative to regulate flow of the refrigerant fluid. The metering valve is located operatively adjacent the flow channel of the thermal head so as to regulate introduction of refrigerant fluid into the thermal head. A controller is operative to control the metering valve for maintaining a predetermined temperature at the temperature controlled surface.
In some exemplary embodiments, the refrigeration system includes a capillary tube having a first end and a second end. The second end of the capillary tube is connected to be in fluid communication with an inlet of the flow channel of the thermal head. The metering valve in such embodiments may be located at the first end of the capillary tube.
The controller is preferably adapted to allow the predetermined temperature to be varied by a user. In this regard, the metering valve may be a pulsing valve operated by a pulse width modulated (PWM) signal. For example, the pulsing valve is preferably actuated at least once per second. The controller itself may be a PID controller.
It will often be desirable to equip the thermal head with at least one heater device also controlled by the controller. For example, the thermal head may be equipped with a plurality of cartridge heaters.
Other aspects of the present invention are provided by an apparatus for controlling the temperature of an electronic device under test. The apparatus comprises a refrigeration system including a compressor and a condenser. The refrigeration system is operative to circulate a refrigerant fluid through a fluid flow loop such that the refrigerant fluid will change between gaseous and liquid states so as to alternately absorb and release thermal energy.
The apparatus further includes a thermal head having a temperature controlled surface. The thermal head defines a flow channel for passage of the refrigerant fluid to thereby function as an evaporator in the refrigeration system. A metering valve is located operatively adjacent the evaporator in the fluid flow loop. The metering valve is operative to regulate introduction of refrigerant fluid into the flow channel of the thermal head for maintaining a predetermined temperature at the temperature controlled surface.
Still further aspects of the present invention are provided by an apparatus for controlling the temperature of an electronic device under test. The apparatus comprises a refrigeration system including a compressor and a condenser. The refrigeration system is operative to circulate a refrigerant fluid through a fluid flow loop such that the refrigerant fluid will change between gaseous and liquid states so as to alternately absorb and release thermal energy.
The apparatus further includes a thermal head having a temperature controlled surface. The thermal head defines a flow channel for passage of the refrigerant fluid to thereby function as an evaporator in the refrigeration system. At least one heater device is operative to supply thermal energy to the thermal head.
A metering valve is adjacent the evaporator in the fluid flow loop. The metering valve is operative to regulate introduction of refrigerant fluid into the flow channel of the thermal head. A controller is operative to control the metering valve and the heater device for maintaining a predetermined temperature at the temperature controlled surface.
Additional aspects of the present invention are provided by a method of maintaining an electronic device under test at a predetermined temperature. One step of the method involves providing a thermal head having both cooling capability and heating capability, the thermal head including a temperature controlled surface in thermal contact with the electronic device. A rate of change of instantaneous power consumption by the electronic device is then determined and compared with a predetermined threshold. If the rate of change exceeds the threshold in a manner indicating that instantaneous power consumption is decreasing, the heating capability of the thermal head is selectively activated. If said rate of change exceeds the threshold in a manner indicating that instantaneous power consumption is increasing, the cooling capability of the thermal head is selectively activated. For example, the cooling and heating capability may be selectively activated by being activated at full operation for a predetermined period of time.
Still further aspects of the present invention are provided by a refrigeration apparatus operative to circulate a refrigerant fluid through a fluid flow loop such that the refrigerant fluid will change between gaseous and liquid states so as to alternately absorb and release thermal energy. The refrigeration apparatus comprises a compressor operative to increase pressure of the refrigerant fluid in the gaseous state. A condenser is also provided, where the refrigerant fluid releases thermal energy while passing therethrough and changes to a liquid state. The refrigerant fluid absorbs thermal energy while passing through an evaporator to thereby change to a gaseous state.
A metering valve is located operatively adjacent the evaporator in the fluid flow loop. The metering valve is operative to regulate introduction of refrigerant fluid into the evaporator. A controller is operative to control the metering valve for maintaining a predetermined temperature at the evaporator.
Other objects, features and aspects of the present invention are discussed in greater detail below.